No motion-induced sensitivity modulation for chromatic gratings.

Abstract

De Valois and De Valois (1991) showed a moving carrier within a static envelope induced a shift in the apparent position of the Gabor patch. It is known that many kinds of motion induce position shifts, however, the underlying mechanism remains unclear. Recently Roach, McGraw and Johnston (2012) showed that motion modulates the sensitivity to an abutting target depending on the relative phase between the target and inducer grating. Phase dependency was found at the leading position but not at the trailing position. However, the relationship between the position shifts and the sensitivity modulation effect remains a subject of debate. We explored this relationship by examining whether a chromatic grating, which can give rise to position shifts, also induces asymmetric phase dependent sensitivity modulation. There were two conditions, equiluminance and luminance. We used a red-green grating in the equiluminance condition and a yellow-black grating in the luminance condition. Equiluminance was measured by the minimum motion technique (Anstis & Cavanagh, 1983). The inducer size was 1 deg x 7 deg and the target size was 1 deg x 1 deg. For both the spatial frequency was 1cpd and the temporal frequency was 5Hz. The relative phase between the inducer and target was manipulated. We used 2AFC staircase to measure the contrast thresholds. We did not find asymmetric phase dependent sensitivity modulation in the equiluminance condition but the contrast thresholds with the motion inducer were higher than that in the no inducer condition, indicating a motion masking effect. We conclude that this modulation effect does not explain the position shifts due to chromatic motion and that sensitivity modulation does not affect position estimation in our visual system.Meeting abstract presented at VSS 2014